1. Field
The following description relates to technology for an orthogonal frequency division multiple access-passive optical network (OFDMA-PON), and more particularly, to technology for an upstream optical link structure of OFDMA-PON and upstream transmission of data, capable of enhancing economic efficiency.
2. Description of the Related Art
Orthogonal frequency division multiplexing, hereinafter referred to as OFDM, is a modulation method for multiplexing high-speed transmission signals with multiple orthogonal narrowband subcarriers.
An orthogonal frequency division multiple access-passive optical network, hereinafter referred to as an OFDMA-PON, which is technology to apply OFDM to a PON, represents one type of a next-generation optical access network for high-speed and long-reach transmission. OFDMA-PON, by using an intensity modulation/direct detection (IM/DD) scheme ensuring cost-effectiveness, maximizes transmission efficiency, enables useful control of network resources, and requires no additional compensation technology for long-distance/high-speed transmission.
Even with the benefits as the above, the commercialization of OFDMA-PON has been delayed due to many reasons, one of which is the absence of a high-speed digital signal processor, hereinafter referred to as a high-speed DSP, enabling real-time operation, and the absence of a data converter (an analog-to-digital converter and a digital-to-analog converter) ensuring speed support for high-speed sampling of several tens of giga bits per second.
Various methods to overcome these shortcomings have been suggested. One of the methods is to multiplex in a manner to reduce physical bandwidth of OFDM signals by using both OFDM modulation and FDM multiplexing so that transmission is achieved at a relatively lower cost and sampling speed of the data converter. Another method is to greatly reduce the size of a fast Fourier transform (FFT), which is required for realizing an OFDM baseband modem, so that a real-time operated DSP is implemented using a field-programmable gate array (FPGA) and etc.